Segmental cast-in-place (including hanging basket pouring, moving formwork pouring, bracket segment pouring) is one of the common construction methods for long-span and extra-long-span bridges.
Due to compactness (and therefore good durability) and excellent mechanical properties (compressive strength ≥150 MPa, flexural strength ≥20 MPa, tensile strength ≥8 MPa, elastic modulus ≥40 GPa), ultra-high performance concrete (abbreviated as UHPC, the same below) has broad application prospects in bridge engineering. When the length of a bridge connection unit is long, due to the limitation of mixing, curing and transportation of UHPC, whether UHPC is used in UHPC-steellightweight composite bridge deck, or in UHPC-steel composite beam or UHPC beam, the connection problems are inevitable.
In calculation of a bridge structure based on the normal bearing capacity limit and normal service limit state, the tensile strength of conventional concrete (including non-ultra-high-strength concrete such as concrete and high-strength concrete) is usually not considered due to its low tensile strength. Rather, the tensile performance of the bridge structures is provided by reinforcing bars or prestressed strands. The bending joint is in the form of a conventional flat joint (i.e., a planar joint) (the segment is subjected to a chiseling process). The high tensile strength of UHPC has an important impact on the economic rationality of UHPC bridges. The steel fiber at the longitudinal seam (joint) is discontinuous, and the tensile strength at the traditional flexural joint is significantly lower than that at the non-joint continuous pouring parts (about 10% of the non-joint continuous pouring parts), making it a weak section (control section) of the UHPC bridge, which requires more prestressed strands to be added to compensate for the tensile strength at the joints. In addition, the discontinuity of the steel fibers at the joints will also have a large adverse effect on the shear bearing capacity of the joints. To this end, many scholars studied the UHPC layers joint in UHPC-steellightweight composite bridge deck and in the segmental prefabricated UHPC beams, and proposed some suggestions for the joint forms suitable for these composite bridge. However, a joint suitable for cast-in-place UHPC continuous bridges has not been reported.
The joints for the UHPC-steellightweight composite bridge deck developed in the previous studies mainly solve the problem of improving the bending capacity (low shear stress) (the tensile capacity of a reasonable shape of the trapezoidal joint can reach 60%˜80% that of a continuous cast-in-place part), and the joints between the segmental prefabricated UHPC beam segments developed mainly solve the problem of improving the shear capacity (the bending resistance is provided by the prestressed strands). However, one of the key problems to be solved by the present disclosure is to improve the shearing and bending between the segmental cast-in-place beam segments (after the beam segment poured firstly reaches a certain strength, then an adjacent beam segment is poured subsequently).
Studies have shown that after 24 to 48 hours of standard curing of the beam segment, steam curing of more than 90° C. for 48 hours is required, which can reduce shrinkage and creep of UHPC and increase concrete strength. However, how to ensure the temperature of on-site steam curing above 90° C. at a low cost has been a major problem for engineers.